Updated for 7.0
On the left-hand side of the screen in the navigation bar, select Group(s) under Member. This will take you here:
Click on the desired group. This will take you here:
In the horizontal navigation bar, click on Members. This will take you here:
Scroll to the bottom and in the box titled Search Members type the full or partial first name, last name, email address, OR membership number that you want to add.
Click the button with the magnifying glass located next to the search bar to search OR click Enter on your keyboard.
A list of potential matches will appear below the search bar.
From the list, click the name of the desired member to add them to the group.
These are samples.